Qt OpenGL 点大小

Question

I am using QOpenGLFunctions with modern OpenGL. I want to draw some GL_POINTS on my window but the point size seems to be really small. Usually, you can change the size of points with

glPointSize(4);

However, this code snippet does not exist in the QOpenGLFunctions wrapper, so I am not sure how to change them.

Drawing GL_TRIANGLES works perfectly fine for me.

I want to draw points to display a point cloud of real-world objects.

Answer 1

If you use QOpenGLFunctions , there is really no glPointSize() available. Why?

The QOpenGLFunctions class provides cross-platform access to the OpenGL ES 2.0 API.

Cross-checking it on khronos.org :

 +--------------+-----------------------------------------------------------------------+ | Function / | OpenGL Version | | Feature Name | 2.0 | 2.1 | 3.0 | 3.1 | 3.2 | 3.3 | 4.0 | 4.1 | 4.2 | 4.3 | 4.4 | 4.5 | +--------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+ | glPointSize | v | v | v | v | v | v | v | v | v | v | v | v | +--------------+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+-----+

So, it is supported for OpenGL but not for OpenGL ES.

There are two possible options:

Option 1: gl_PointSize

In OpenGL ES, you may use the GLSL shader variable gl_PointSize instead.

(I found this "accidentally" while searching for appropriate doc. links – haven't known this before nor ever used it.)

derhass provided the additional hint that this might be used with OpenGL (non-ES) as well if enabled by glEnable(GL_PROGRAM_POINT_SIZE) .

GL_PROGRAM_POINT_SIZE

If enabled and a vertex or geometry shader is active, then the derived point size is taken from the (potentially clipped) shader builtin gl_PointSize and clamped to the implementation-dependent point size range.

Option 2: Use an alternative QOpenGLFunctions_??? class

Instead of QOpenGLFunctions , you may explicitly use a non-portable alternative (assuming you don't need to support phones, embeddeds or something like this).

The best overview in Qt doc. I could find: QAbstractOpenGLFunctions .

Answer 2

As suggested derhass, first enable the point size with this line in your C++ code (not the shader):

glEnable(GL_PROGRAM_POINT_SIZE);

Then as suggested Scheff, in your vertex shader code, add the gl_PointSize builtin function. So for example if you wanted a size of 12 for a point, use it like that.

// main from your vertex.glsl shader (not from your main.cpp!)
void main() {
    ...
    gl_PointSize = 12;
    ...
}